This invention relates to diesel engines, and more particularly to high-pressure fuel supply pipes for diesel engine fuel injectors in a common rail fuel system.
In one class of diesel engines with common rail fuel systems, fuel is supplied to the engine fuel injectors through fuel pipes extending within the cylinder head. Each fuel pipe has a frusto-conical end surface in pressure engagement with a mating recess in a side surface of the fuel injector, to establish a sealed connection between the fuel pipe and the side surface of the fuel injector.
A nut is threaded into the cylinder head to exert an axial force on the fuel pipe, whereby the fuel pipe end surface is pressured against a recessed side surface of the fuel injector. During initial movement of the nut the frictional engagement between the nut and the fuel pipe tends to rotate the fuel pipe around the pipe longitudinal axis. Such pipe rotation tends to disturb the surface contact between the pipe end surface and the recessed area of the fuel injector so as to potentially produce fuel leakage at the pipe end surface. Therefore, it is necessary to provide some mechanism for preventing the fuel pipe from rotating while the nut is being turned to apply an axial force on the fuel pipe.
The present invention relates to a key-slot relationship for preventing rotation of the fuel supply pipe in the cylinder head. In the preferred practice of the invention, the key slot is formed in a sleeve that is press fit in a bore in the cylinder head. The sleeve has a relatively precise well thickness so that the slot has a relatively close dimension radial relationship to the key. The key can take various forms, e.g., a bar having a half moon profile, or a ball, or a cylindrical pin. The invention relates more particularly to a slotted sleeve for forming the key slot.
In a prior art arrangement the key slot was provided by a groove formed directly in a bored hole in the cylinder head. The groove had a semi-circular cross section. The key was a ball having a press fit in a socket in a side surface of the fuel pipe. However, it was determined that the circumferential load forces on the key tended to degrade the slot surfaces at the mouth of the slot, so that the ball-shaped key tended to exert a radial cam force on the slot surface. In some instances the ball-shaped key imposed a radial load on the fuel pipe, whereby the fuel pipe experienced an undesired local radial distortion.
The undesired radial distortion of the fuel pipe results from a tolerance build up on the various machined surfaces. There is a first tolerance inaccuracy on the diameter of the bore that slidably supports the fuel pipe. There is a second tolerance inaccuracy in the semi-circular cross section groove that forms the key slot. This second inaccuracy is particularly troublesome, in that it can -produce an undesired looseness of the ball-shaped key in the key slot or an undesired frictional resistance between the key and the key slot surfaces.
The use of a slotted sleeve as the mechanism for forming the key slot, is advantageous in that the sleeve wall thickness automatically provides the radial dimension of the key slot, so that inaccuracies or inconsistencies of the slot machining process do not adversely affect the radial dimension of the key slot.
The present invention relates to the employment of a sleeve insert in an engine cylinder head for providing a key slot that prevents rotation of a fuel pipe in the cylinder head. Specific features of the invention will be apparent from the attached drawings and description of an illustrative embodiment of the invention.